The present invention generally relates to a counter reset mechanism employed in an image forming apparatus and more particularly, to a counter reset arrangement capable of resetting a counter which is employed to detect or keep count of the remaining useful life of consumable elements such as a photoreceptor, a cleaning unit or the like at a time when the cartridge containing the elements is mounted in or dismounted from the image forming apparatus.
According to a recent trend of image forming apparatus such as copying apparatus or the like towards small size and minimizing maintenance requirements, the image forming apparatus is constructed so that a photoreceptor drum and its environmental parts are integrally incorporated into a cartridge so that they are replaceable at the time when service life thereof is about to expire or has expired. In such a construction the environmental parts i.e., a corona charger, a cleaning unit and the like are integrally incorporated together with the photoreceptor drum into a cartridge. Thus, when the photoreceptor drum needs to be replaced or when the cleaning unit has accumulated full amount of superfluous toner particles, a user must simply replace the entire cartridge without necessity for calling servicing personnel. Accordingly, the user may advantageously readily deal with such situation by himself without the necessity of any servicing personnel for maintenance.
Meanwhile, in a cartridge of this kind, the service life of the photoreceptor drum is detected by a counter disposed on the main body of the copying apparatus in accordance with the amount of use thereof and, whenever the counter has reached a predetermined amount of use, the user is urged to replace the photoreceptor drum upon indication of the condition thereof on an operation panel. When the cartridge of the type having a counter which can not be reset is in use, however, the user can occasionally forget to record indicated value of the counter at the time of replacement of the cartridge. Furthermore, even in the case where a counter reset arrangement capable of resetting the counter is provided in the cartridge, the user may inadvertently fail to reset the counter by actuation of the counter reset arrangement. For the purpose of avoiding the above described problems, in one of the conventional copying apparatus, a protruding piece which can be broken off is formed on the end portion of a magazine, i.e., the cartridge including the photoreceptor drum, with the counter being mounted in the main body of the copying apparatus so as to confront the protruding piece. In the copying apparatus having such construction, the counter reset arrangement is automatically operated in the case of mounting the magazine into the main body, and the protruding piece is broken off the magazine so as not to further affect the counter reset arrangement. Such apparatus is disclosed, for example, in Japanese Utility Model Laid-open Application (Jikkaisho) No. 59-176059.
In the apparatus of this kind, however, since the protruding piece is broken off by being forcibly pressed towards the counter when the magazine is mounted, in the case where the protruding piece is made of synthetic resin and drops inside the main body of the copying apparatus, it occasionally contacts a liquid accommodated therein, thus resulting in an undesirable chemical reaction. In the case where the protruding piece is made of metallic material, it occasionally bites into rollers or the like to disadvantageously damage them. Moreover, this kind of copying apparatus is so designed that when the magazine has been once mounted therein, the same magazine can no longer execute the reset operation and thus cannot be removed from apparatus until the replacement thereof is required. Accordingly, there exists an inconvenience such that the operation of the counter reset arrangement cannot be checked during production process.